1. Field of the Invention
The present invention relates to a high-magnification zoom lens, and in particular, to a high-magnification zoom lens having both a comparatively short lens system and superior image composing capability.
2. Description of Related Art
In recent years, together with the shift to zoom lenses having higher magnification and a reduced overall size, various types of zoom lenses have been introduced. In particular, high-magnification zoom lenses that have a magnification changing ratio of 3 to 5 times or more, a field angle of 70.degree. and a telephoto range, are known. These lenses include, arranged in order along the optical axis from the object side (i.e., the side closest the object being photographed), a first lens group with a positive refractive power, a second lens group with a negative refractive power, and a third lens group with a positive refractive power.
In the conventional 3-group zoom lenses described above, however, the refractive power of each lens group must be increased to provide greater magnification and a wide angle region with a wider field angle. Similarly, to provide the same magnification and wide angle region in a zoom lens having a more compact size, the refractive power of each lens group must also be increased. As a result, the lens weight increases, and the manufacture of a lens surface having a high refractive power becomes very difficult. In addition, maintaining sufficient image composing capability over the range from the wide angle setting to the telephoto setting is difficult. Further, the size of the first lens group can become quite large, which is undesirable.